Join Date: Sep 2013
Location: San Francisco, CA & Bangkok (Home)/Lawrenceville & Switzerland (Boarding School)/Baltimore, MD (College)
Programs: DL DM, AL MVPG 75K, SQ Gold, BA Silver, HH Diamond, Hyatt Globalist, Marriot Plat, Hertz Pres Circle
Posts: 599
In my recent experience, DL will interline bags for their sky team partners. Had no problem doing it from DL to AF a few weeks ago. However, I was told they weren't able to do it with Alaska despite being frenemies. You may have more luck with Virgin Atlantic because of the code shares they have.
In regards to being protected, I have always been protected by DL when having 2 separate tickets on partner airlines. Heck, my last issue was in December, and the flight was delayed from SFO-JFK and I missed my Amtrak train, and they even booked me on DL flight JFK-PHL